1. Field of the Invention
The present invention relates to a heart pacemaker.
2. Description of the Prior Art
An existing cardiac pacemaker consists of a power source and electronic circuitry which together constitute a pulse generator housed within a hermetically sealed metal capsule. The metal capsule is arranged to be inserted within a patients body normally near one of the pectoral muscles. An insulated lead having its proximal end connected into a receiving port of the metal capsule so as to provide a direct connection with the pulse generator, has its distal end connected to one or more bare metal electrodes which are located inside the patients heart. Typically, such transvenous electrodes are positioned in the right ventricle and deliver stimulating impulses to the endocardium. This was first successfully performed by Lagergren et al. at the Karolinska Institute in Stockholm, Sweden, 1962. Prior to this the stimulating electrodes were attached to the epicardium by thoracotomy for both external and implantable pacemakers.
Transvenous electrodes suffer from a number of problems one of which is a loss of synchronous mechanical contraction of the left and right ventricles. This is referred to as pacemaker induced left branch block type conduction disturbance and is recognized by a lengthening of the QRS complex. The resultant reduction in left ventricular chamber performance is indicative of a reduced cardiac output, especially at higher heart rates as with rate responsive physiological pacemakers. The cause of the pacemaker induced left bundle branch block is the positioning of the stimulating electrode on the free wall of the right ventricle. This right ventricular pacing causes an intraventricular delay in the transmission of stimulating impulses to the left ventricle. In a normal healthy heart the ventricles are stimulated to depolarization by nerves that are found in both the left and right ventricles, thus ensuring synchronous isovolumic systole occurs in both ventricles in every heart beat. The single transvenous electrode positioned in the right ventricle cannot replicate this process.
Conventional pacemakers using electrodes placed transvenous in the right ventricle of the heart also suffer from a number of other problems. Relatively long conductive leads are used to connect the implanted electrode to the pulse generator and the electrode, requiring the generation of higher voltages and resulting in a large drain on the power source. This shortens the life of the pacemaker.
It is necessary to surgically implant the electrode into the heart. This can be an expensive procedure, which in conventional transvenous electrodes, requires the provision of expensive equipment to perform fluoroscopy for positioning of the electrode. The expense of the procedure limits application.
Further, generally only a single electrode is implanted. This single electrode is used both for sensing cardiac activity and providing pacing pulses. In pacing at higher rates, polarization of the electrode site increases due to the reduced time between dispersion of the voltage of polarization. Pacing voltage must therefore be increased to overcome the polarization potential and apparent increase in impedance. This, again, results in an increased drain on the power source.
Further, coupling the sensing and pacing functions in a single electrode results in the possibility of local polarization interfering with the sensing function.
Yet a further problem is movement of the electrode away from the original implantation side. This results in the incorrect stimulation of the cardiac tissue.
Further, an operation would be necessary to correct the electrode position. Positioning of the electrode when only a single electrode is used is very important. Any error can lead to problems.
A method of pacing both ventricles has been proposed by Mower (U.S. Pat. No. 4,928,688). The Mower device uses two transvenous electrodes, one positioned in the usual place in the right ventricle and a second electrode positioned in the coronary sinus about the left ventricle (derived from U.S. Pat. No. 4,458,677 to McCorkle). At least one ECG amplifier is arranged to separately detect contraction of each ventricle and a stimulator is then activated for issuing stimulating pulses to the electrodes in an attempt to assure a simultaneous contraction of both ventricles. The device is designed to restore substantially simultaneous contraction of both ventricles where there is a bundle branch block to either right or left ventricle or a slow conduction to either. It does not refer to correction of pacemaker imposed left bundle branch block and uses electrodes with the dual functions of sensing and stimulation. There is no disclosure of an arrangement for restoring a uniform spread of the depolarization pattern at the heart as in nature. Instead, two foci of stimulation are employed, one in the right ventricle near the apex and the other high up the heart on the left ventricular of free wall. Further, the surgical procedure necessary to implant an electrode in the coronary sinus is complex and difficult. Furthermore, Mower provides no solution to the problems of using single electrodes connected by relatively long leads.
From a first aspect, the present invention provides a heart pacemaker, comprising a base member mounting a plurality of pacing electrodes, the base member being adapted to fit to the apex of the heart such that the pacing electrodes are positioned about the apex of the heart and able to provide stimulation to the apex of the heart, and pulse generator means for causing the electrodes to provide cardiac stimulating pulses to the apical area.
The base member preferably forms part of a hermetically sealed body comprising pulse generator circuitry and a power source for providing the pacing function. The entire body is preferably of such size that it can be placed at the apex of the heart in between the diaphragm and the heart. Surgical placement of such a device may be a fairly simple procedure and can preferably be performed by today's endoscopic techniques.
The base member is preferably shaped to conform to the apical area of the heart so that electrodes on the surface of the pacemaker contact heart tissue. The base member preferably comprises a concave surface, the electrodes preferably being placed on the concave surface is preferably designed to "hug" the apical area.
The apex of the heart is where the free walls of left and right ventricles meet the intraventricular septum. This left ventricular apex is more prominent than that of the right ventricle at the apical area. By positioning the plurality of the electrodes about this apical area, the electrodes are preferably able to provide a depolarization wave that spreads up and into the whole heart in an even fashion, in a sense mirroring the excitement pattern of a healthy heart. This will preferably result in both ventricles and the septum receiving a stimulating impulse substantially simultaneously. Substantially simultaneous mechanical activity of both ventricles can then occur with support from a rigid base formed by a stiffening of the intraventricular septum of the apex. This contractile pattern will preferably help to overcome compromises to hemodynamics associated with the asgnergic contractile pattern of left bundle branch block and the similar condition imposed by the conventional intraventricular pacemakers. Pulsing the apex of the left ventricle the apex of the left ventricle being more prominent of the apex of the heart than the apex of the right ventricle provides a hemodynamic advantage over conventional pacing.
The heart pacemaker of the present invention is preferably an epicardial extra-cardiac device, the electrodes contracting the surface of the heart tissue and not being implanted therein. Provision of a hermetically sealed body containing the pulse generator circuitry and power source and arranged to be placed next to the heart preferably does away with the need for long connecting leads as employed in conventional intracardiac pacemakers, such as disclosed in the Mower patent.
An array of electrodes is preferably provided on the surface of the base member. Preferably any number of the electrodes may be selected to provide pacing pulses, in order to provide the most clinically appropriate stimulation. Further, sensing electrodes are also preferably placed in an array and are preferably separate from the pacing electrodes.
Preferably, selection means are provided for selecting which sensing and/or pacing electrodes to use. The selection means may comprise an electrode multiplexer and control means for determining which electrodes are to be selected for sensing and/or pacing. Periodic selection re-selection of sensing/pacing electrodes may be carried out by telemetry. For example, a cardiac specialist utilizing telemetry, may first of all apply a number of tent pulses via selected electrodes to determine the most optimum electrodes to use to provide the most clinically appropriate stimulation. This "calibration" may be done on installation of the pacemaker and also at periodic intervals. Conventional pacemakers are calibrated (eg. pulse-width, pacemaker voltage, etc.) by telemetry and the selection process in accordance with the preferred embodiment of the present invention could also take place at this time.
A further option is that selection could be determined internally of the pacemaker by an appropriate programmed control means constantly monitoring cardiac response and having the facility to select any of the pacing/sensing electrodes to determine the best response.
Furthermore, a control means may control the selection means to switch constantly between preselected electrodes in order to reduce polarization effects.
A further technique for reducing polarization of the electrode area may also be applied. The polarity of pacing pulses may be reversed, either periodically or on alternate pulses. This technique is described in copending patent application PCT/AU92/00219, and the disclosure of that application is incorporated herein. Separation of the sensing electrodes from the pacing electrodes reduces possible polarization effects on sensing electrodes.
Reduction of polarization enables lower than conventional pulsing voltages to be used, resulting in less drain on the power source.
Because, preferably, no relatively long leads are used to connect the electrodes to the pulse generator (the pulse generator being preferably within the hermetically sealed capsule the base member of which mounts the electrodes) the problems discussed above in relation to relatively long leads do not exist. The pacemaker of the present invention can therefore preferably be run at low voltages, resulting in extended lifetime.
The electrodes on the surface of the base member preferably are not implanted in the heart tissue. They preferably contact the surface of the heart, providing stimulation epicardially. This preferably overcomes the problems associated with surgical implantation of electrodes. If the pacemaker and electrodes should shift position, then recalibration to select other electrodes to provide stimulating/sensing functions to obtain the most clinically appropriate stimulation can be carried out. There will preferably be no need for surgery to relocate any electrodes.
A means for sensing physical activity of the patient is preferably provided in the pacemaker and means for adjusting the response of the pacemaker in dependence upon the physical activity of the patient. The pacemaker can thus respond to an increase in physical activity of the patient, for example, by increasing the frequency of pacing pulses to the heart. Physical activity is preferably sensed by a sensor placed on the diaphragm to monitor changes in breathing rate, depth, etc. of the patient. The sensor is preferably an electrode which is placed on an opposite face of the hermetically sealed chamber to the base member mounting the sensing and pacing electrodes.
Cardiac pacing can therefore be determined to suit the physiological requirements of the patient. The apical stimulation provided by the pacemaker preferably allows for a good hemodynamic response in response to changes in physical activity.
Preferably, each electrode is formed by a pair of capacitive plates and a dielectric. Each electrode preferably comprises a first capacitive plate on the outer surface of the base member, a dielectric, which preferably comprises the base member itself, and a second capacitive plate on the inside surface of the base member, i.e. within the pacemaker chamber/housing. The second plate is connected to the pulse generator means.
The employment of a capacitive construction for the electrodes preferably enables stimulation and/or sensing of cardiac tissue from within a hermetically sealed pacemaker, thereby eliminating any need for direct connection via a long lead or through the pacemaker housing walls thereby eliminating current leakage and fragile lead throughs requiring a hole in the pacemaker housing walls.
The pulsing and sensing electrodes are preferably arranged in a ring array formation on the base member.
Capacitive plates on the outer surface of the base member are preferably made from tissue compatible materials, such as carbon fibre or platinum black.
Preferably, where the pacemaker comprises a hermetically sealed housing, the housing has an outer peripheral layer that comprises tissue compatible material which is light weight and non-metallic/insulating material.
Where physical activity is sensed by a diaphragm sensing means, the diaphragm sensing means may be arranged to contact the diaphragm on its sternal region approximately below the sixth rib to approximately the junction between the underlining intercostal muscles and the diaphragm.
The diaphragm sensing means may sense sound levels generated by the diaphragm.
Preferably, the diaphragm sensing means senses electrical activity near the intercostal muscle junction.
The pacemaker is preferably provided with a control means in the form of a processing means for controlling the pulse generator.
The processing means may be arranged to receive electrical signals from the diaphragm sensing means and process the electrical signals to determine the desired heart rate.
Preferably the processing means is arranged to receive electrical signals from the diaphragm sensing means and process the electrical signals to produce signals indicative of the respiration rate of the diaphragm.
The processing means may be arranged to control the pulse generator to produce pulses indicative of the required heart beat rate based on the respiration rate sensed by the diaphragm sensing electrode.
Preferably the processing means comprises an electrical converter for converting a sensed signal from the diaphragm sensing means to a positive or negative going bias voltage which is arranged to alter the pulsing rate of the pulse generator.
The diaphragm sensing means may sense a current or voltage indicative of the respiration rate.
The processing means may comprise a diaphragm sensing system for receiving a sensed signal from the diaphragm sensing means.
The processing means may further comprise a CPU connected with the diaphragm sensing system.
The diaphragm sensing system can comprise an electrical transducer for converting signals received by the diaphragm sensing means to electrical signals compatible with the CPU.
The CPU preferably controls the pulse generator.
Preferably the CPU outputs data relating to the respiration rate.
The CPU may be programmed to control the pulse generator to produce pulses between a typical rate of 120 and 60 pulses per minute, i.e., produce a heart beat of 120 to 60 beats per minute depending on the sensed respiration rate.
The diaphragm sensing system may be arranged to sense through the diaphragm sensing means, changes in breathing rate, breathing depth or diaphragm velocity or changes in noise levels in the environment surrounding the diaphragm.
The processing means may comprise an output controller connected with the CPU and controlled by the CPU to control the pulse generator by converting signals from the CPU to a form compatible for controlling the pulse generator.
The processing means may comprise a telemetry means for receiving transmission signals from outside the pacemaker and communicating the signals to the CPU.
The telemetry means may comprise an antenna for receiving transmission signals.
The telemetry means may comprise a transmitter for transmitting signals through the antenna to an external receiver.
Preferably the CPU is arranged to be remote controlled by transmission signals received through the telemetry means.
Preferably the CPU can be instructed by the remote control to carry out self diagnostic steps which result in information which is arranged to be transmitted through the telemetry means to the external receiver.
It is preferred that the external receiver be a data processing means which is linked to a receiving antenna through a telemetry system.
Preferably the data processor comprises a keyboard which allows a user to control the data processor to send transmission signals to control the CPU of the pacemaker.
Preferably the pacemaker container is part hemispherical in shape with the first surface being a concave surface and the second surface being a convex surface.
The pacemaker may be arranged to be attached to the apex of a heart by an attachment device.
Preferably the attachment device comprises a body and a peripheral portion, the peripheral portion being arranged to be attached to the heart, the body portion being arranged to support the pacemaker.
From a second aspect, the present invention provides a method of pacing the heart, comprising the step of providing pacing pulses to the apical area of the heart.
Pacing pulses are preferably provided by a plurality of electrodes positioned about the apical area of the heart. The method of this aspect of the present invention may be carried out by the pacemaker previously defined.
Preferably, the method includes the step of selecting between a number of available pacing/sensing electrodes to provide optimum cardiac output.
Preferably, the method further comprises the step of sensing the physical activity of the patient and adjusting the pacing of the heart in response to the degree of physical activity. This step preferably comprises sensing activity of the patients diaphragm.
The area around the intraventricular septum may be stimulated slightly before polarizing the three walls of the ventricles, whereby to ensure a rigid septum as the ventricles are polarized.
From yet a further aspect, the present invention provides a heart pacemaker comprising a pacing electrode, pulse generator means for causing the electrode to provide cardiac stimulating pulses, a sensing means for sensing the physical activity of the patient and means for adjusting pacing of the heart by the electrode in response to variations in the physical activity of the patient.
Sensing means is preferably arranged to sense activity of the patient's diaphragm and is preferably an electrode adapted to contact the patient's diaphragm.
The pacemaker of this aspect of the invention may include any or all of the features of the pacemaker defined in relation to the first aspect of the invention above.
The present invention yet further provides a method of pacing a heart, comprising the steps of providing pacing pulses to the heart, sensing the physical activity of the patient, and varying the pacing of the heart in response to variations in the physical activity of the patient.
The method of this aspect of the invention preferably comprises the step of sensing the physical activity of the patient's diaphragm.
The method of this aspect of the invention may include any or all of the method steps of the first method aspect of the invention defined above.
The present invention yet further provides a heart pacemaker, comprising three or more pacing electrodes arranged to contact the heart to provide pacing pulses to the heart, pulse generator means for causing the pacing electrode to provide cardiac stimulating pulses and selection means for selecting one or more of the three or more electrodes to provide pacing pulses to the heart at any particular time, whereby one, some or all of the pacing electrodes may be used to provide stimulation as clinically appropriate.
The pacemaker of this aspect of the invention preferably also comprises a plurality of sensing electrodes, and the selection means is preferably arranged to select one or more of the sensing electrodes to provide sensing signals.
The pacemaker of this aspect of the invention may include any or all of the features of the aspects of the invention defined above.
The present invention yet further provides a method of pacing the heart, comprising placing three or more pacing electrodes in contact with the heart, and selecting one or more of the three electrodes to provide pacing pulses to the heart at any particular time, whereby one, some or all of the pacing electrodes may be used to provide stimulation as clinically appropriate.
The method of this aspect of the invention preferably comprises the further step of placing one or more sensing electrodes in contact with the heart to sense electrical activity of the heart, and selecting which of the sensing electrodes to use to provide sensing signals.
The method of this aspect of the invention may include any or all of the features of the aspects of the invention defined above.
The present invention yet further provides a heart pacemaker, comprising a housing containing a pulse generator means for causing pacing electrodes to provide cardiac stimulating pulses, the housing comprising a base member mounting at least one pacing electrode, the pacing electrode being constructed in the form of a capacitor and comprising a first capacitive plate on an outer surface of the base member, a dielectric and a second capacitive plate on the inner surface of the base member within the housing.
The dielectric is preferably formed by the base member itself.
The pacemaker of this aspect of the invention may include any or all of the features of the aspects of the invention previously defined.
The present invention yet further provides a heart pacemaker, comprising a hermetically sealed housing containing pulse generator means for causing pacing electrodes to provide cardiac stimulating pulses to the apical area of the heart, the housing comprising a base member mounting a plurality of pacing electrodes and being adapted to fit to the apex of the heart such that the pacing electrodes are positioned about the apex of the heart, the housing comprising a further member mounting a diaphragm sensing electrode adapted to contact the diaphragm and provide information relating to the physical activity of the patient, and means for adjusting pacing in response to variations in the physical activity of the patient.
The pacemaker of this aspect of the invention may include any or all of the features of the aspects as previously defined.
The present invention yet further provides a heart pacemaker, comprising a member mounting at least one electrode, the member being adapted such that the electrode may contact the surface of the heart but is not surgically implanted within heart tissue.
The pacemaker of this aspect of the invention may include any or all of the features of the aspects of the invention previously defined.
According to another aspect of the present invention there is provided a pacemaker for a heart, comprising at least one stimulating electrode, a pulse generator means for generating a series of pulses, the pulse generator means in use being arranged to deliver pulses of opposite polarity to the or each stimulating electrode.
Preferably the pulses are periodic.
The pulses may comprise an equal number of positive and negative pulses.
The pulses may also comprise a sequence of positive pulses followed by a sequence of negative pulses.
In a preferred embodiment of the present invention each pulse is followed by another pulse of opposite polarity.
Preferably each pulse of opposite polarity has a substantially identical wave form.
Each pulse may have a substantially identical wave form.
According to another embodiment the root mean squared (RMS) value of each waveform is identical.
The pulses preferably are current or voltage pulses.
Each pulse is preferably generated at successive equally spaced time intervals.
A sequence of pulses may be generated at successive equally spaced time intervals.
The pulse generator means preferably comprises a pulse generator.
The pulse generator means can comprise switching circuitry for switching pulses from positive to negative.
It is preferred that the pulse generator means comprises a timer circuit for determining the time interval separating each pulse.
The timer circuit may be connected with the pulse generator and the switching circuit.
Preferably the pulse generator means comprises a battery connected to the timer circuit and pulse generator.
According to an alternative form of the present invention the pulse generator is connected with an output circuit of the pulse generator means.
The switching circuit may also be connected with the output circuit.
The pacemaker may be a self-contained unit which is arranged to be attached to a heart.
The timer circuit can be controlled to vary the time interval between successive pulses.
The pulse generator means can be controlled to vary the amplitude of each pulse generated.
Preferably when in use the pacemaker substantially eliminates polarization at the or each stimulating electrode.